Keeping your stones connected as solidly as necessary with as few stones as possible is something which any go player will have to learn in order to improve.
Here are a list of common connections used, as well as some shapes which you should be able to recognise.
See also elementary moves, haengma, shape, how the cut is protected.
Dieter: I have never liked this page, yet it is referenced from many pages. I'd like to split it up into connecting techniques and other shapes.
Gabaux: I have read somewhere about harmonic shapes. Does anybody have further information what is this technical term? Or can somebody show some such shapes?